BRITAIN faces a "very, very serious threat" of an imminent Paris-style attack and security services are working "around the clock" to thwart any plots on UK soil, Europe's top police officer has warned.

ISIS fighters

Iraq and Syrian jihadists, including the Paris and Brussels attacks suspects.

Europe's current threat level is at its highest for 10 years in the wake of attacks in the French capital last November and intelligence that suggests an attack is highly likely.

The former MI5 officer also used the warning to highlight apparent dangers of Britain leaving the EU.

The British terror chief said it would be "difficult for the UK to replace what it currently relies on in the EU with arrangements that would be as effective and as cost efficient as well".

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Rob Wainwright, director of Europol - the EU’s law enforcement agency

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Rob Wainwright with the Dutch PM at Europol's HQ

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London was struck by a terror attack in 2005

On Monday, the country's head of counter-terrorism warned that ISIS jihadis were planning "enormous and spectacular" terror attacks.

Assistant Commissioner Mark Rowley, the National Policing Lead for Counter Terrorism at Scotland Yard, said the extremist organisation was broadening its terror campaign to attack "Western lifestyle" targets.

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He said: "In recent months we've seen a broadening of that, much more plans to attack Western lifestyle, and obviously the Paris attacks in November.

"Going from that narrow focus on police and military as symbols of the state to something much broader. And you see a terrorist group which has big ambitions for enormous and spectacular attacks, not just the types that we've seen foiled to date.

"You see a terrorist group that whilst on the one hand has been acting as a cult to use propaganda to radicalise people to act in their name ... you also see them trying to build bigger attacks."